The present invention relates to a clay-titanium tetrachloride catalyst and the method for preparation of the catalyst.
Polymer/layered silicate nanocomposite is a new excitement in the field of polymeric materials. Relatively small amount (xe2x89xa65 wt %) of nanometer-sized dispersed clay layers in the polymer matrix not only significantly raises the mechanical and thermal properties of the material, but also bestows on the materials additional benefits, such as reduced gas permeability, increased dimensional stability and enhanced flame retardancy, without substantially raising the density or damaging light transmission of the corresponding neat resin. Example of such disclosures are (1) E. P. Giannelis, Adv. Mater. 1996, 8, 29. (2) Z. Wang, T. J. Pinnavaia, Chem. Mater. 1998, 10, 3769. (3) Y. Kojima, A. Usuki, M. Kawasumi, A. Okada, Y. Fukushima, T. Kurauchi, O. Kamigaito, J. Mater. Res. 1993, 8, 1185.
The great economic values of polyolefin nanocomposites are foreseen in potential applications in various areas; nevertheless, the preparation of such composites is still in its exploration stage. Melting intercalation of an organically modified silicate with polyolefin is an approach having been receiving intensive attention, the steps of modifying the silicate, polarizing the polyolefin or its oligomers and the chemical or physical deterioration of the virgin components during mixing process may offset the benefits of the silicate to some extent. In situ polymerization is an alternative approach for preparation of polyolefin nanocomposites, which involves intercalation of a silicate by a metallocene or Ziegler-Natta catalyst, followed by polymerization of an olefin.
In situ polymerization overrides entropic and enthalpic barriers associated with intercalating nonpolar polyolefin with polar silicates; the strongly polar nature of layered silicate is still to be considered for mechanism with metallocene or Ziegler-Natta catalyst. The seemingly tolerable Brookhart catalyst toward polarity and moisture was found to have a quite low activity in ethylene intercalation polymerization (J. S. Bergman, H. Chen, E. P. Giannelis, M. G. Thomas, G. W. Coates, Chem. Commun. 1999, 2179.). To protect the active sites from poisonous inner surface of the silicate, O""Hare and coworkers first treated the layered silicate with a large amount of MAO, and then immobilized the metallocene catalyst on the MAO modified silicate. Unfortunately, in situ polymerization with this catalyst gave only propylene oligomers in low activity [(1) J. Tudor, L. Willington, D. O""Hare, B. Royan, Chem. Commun. 1996, 2031. (2) J. Tudor, D. O""Hare, Chem. Commun. 1997, 603.]. WO 99/47589 disclosed a method for preparation of polyolefine nanocomposite by in-situ polymerization. The polyethylene nanocomposite materials thus obtained possess both high tensile strength and high modulus. The method comprises the steps of: 1) dispersing layered silicate clay with water, and then removing water by freeze-drying to lower the polarity of the clay; 2) treating the clay thus obtained with a large amount of methyl aluminoxane (MAO) and removing the excess of MAO by washing; 3) adding metallocene catalyst to the MAO treated clay in heptane; 4) allowing ethylene to polymerize. The method has the following drawbacks: 1) freeze-drying treatment of clay is a time-consuming and expensive process; 2) consumption of large amount of expensive MAO is required, since [MAO]/[Ti] ratio is in the range of 1000xcx9c greater than 3000; 3) the activity of metallocene catalyst is greatly reduced.
It is one object of the present invention to provide a clay-titanium tetrachloride catalyst used for the preparation of polyolefine/clay composite materials.
It is another object of the present invention to provide a method for the preparation of the clay-titanium tetrachloride catalyst of the present invention.
The present invention provides a method for the preparation of polyolefine/clay composite materials by using the catalyst of the present invention. In this method, Ziegler-Natta catalyst is supported within the layers of layered silicate clay and the olefin is directly polymerized into polyolefine nanocomposite material.
The present invention provides a clay-titanium tetrachloride catalyst used for the preparation of polyolefine/clay composite materials, comprising the components of:
1) a phyllosilicate, including smectite clays, such as sodium montmorillonite and calcium montmorillonite, hectorite clay etc. Both original and chemical or physical modified clays can be used.
2) a magnesium compound, such as MgCl2, Mg(OR)2 or MgR2, wherein R is an alkyl group having 1-8 carbon atoms;
3) an alcohol compound which is capable of dissolving the magnesium compound, such as aliphatic alcohols having 1-8 carbon atoms, for example, methanol, ethanol, propanol, butanol, isopropanol and/or isobutanol;
4) titanium tetrachloride TiCl4; and optionally
5) an electron-donor reagent selected from the group consisting of aromatic esters and aromatic group substituted or cycloalkyl group substituted alkoxy silane, such as ethyl benzoate, butyl benzoate, diethyl phthalate, dibutyl phthalate, diphenyl dimethoxy silane and/or triphenyl methoxy silane.
The present invention further provide a method for the preparation of the clay-titanium tetrachloride catalyst, comprising the steps of:
1) dissolving a magnesium compound as defined above in an aliphatic alcohol to a concentration of 0.1 g-10 g/100 ml to obtain a transparent and stable solution, and adding an electron-donor reagent with a mole ratio of [Mg]/[electron-donor reagent] at 1:1 to 1000:1 when the electron-donor reagent is used;
2) adding a clay at an amount of 0.01-10 g per millimole magnesium compound into the aliphatic alcohol solution of the magnesium compound with stirring;
3) filtering off the aliphatic alcohol and removing the residual aliphatic alcohol at reduced pressure or by alcoholysis using chemical method (1-10 mmol/g solid alkyl aluminum compound can be used for the alcoholysis reaction);
4) adding TiCl4 into the solution with stirring to obtain a [Ti]/[Mg] molar ratio in the range of 1/10 to 1000/1;
5) filtering the solution and washing the solid powder thus obtained with an inert solvent until no transition metal ion is detectable in the filtrate, and drying the powder.
The catalyst system of this invention uses alkyl aluminum compound with the formula of AlRnCl3xe2x88x92n as the cocatalyst or alcoholysis reagent, wherein R is an alkyl group having 2-8 carbon atoms and n is an integral of 2 or 3.
The preparation of polyolefine/clay composite materials by using the catalyst of the present invention can carried out under slurry polymerization conditions. Saturated alkane or cycloalkane is used as the solvent. [Al]/[Ti] mole ratio is in the range of 3 to 300 and the polymerization temperature is xe2x88x9230xcx9c90xc2x0 C. When polypropylene nanocomposite material is prepared, the catalyst should contain inner electron-donor reagent and/or outer electron-donor reagent. When polyethylene nanocomposite material is prepared, electron-donor reagent can be used or not be used. The tensile strength of nanocomposite materials thus obtained is 32-50 Mpa, and the Vicat temperature is 131-220xc2x0 C.
The catalyst system of the present invention could be used to prepare nanocomposite materials of polyethylene, polypropylene, other polyolefins and their copolymers, and can be used in slurry polymerization, gas phase polymerization and bulk polymerization processes.
This invention eliminated the requirements to use the expensive freeze-drying process and expensive MAO. Therefore the costs are very much reduced compared with that using metallocene catalyst systems. In addition, the processes for synthesis and polymerization are similar to those currently used in the industrial production of polyolefine, thus it would be much easier to be industrialized. In comparison with melt blend method, the method of the present invention uses clay-containing Ziegler-Natta catalyst to polymerize olefine directly into polyolefine nanocomposite materials, and by this way, time consuming and tedious post-processing and/or post-treatment can be avoided.